In the oil and gas industry, there are a number of well known systems for stimulating multiple zones or stages in a single trip. One such system utilizes balls, dropped from surface, to engage a sleeve in a sleeve valve blocking ports in a completion string to open the valves to permit stimulation of the formation through the ports. Ball seats on the sleeve valves engage the balls and pressure in the bore acts thereon to release and shift the sleeve downhole. Operations are generally performed from the toe of the wellbore to the heel. Typically, ports in a toe sub are opened, such as by pressure actuation, to permit pumping at least a first of the series of balls through the completion string.
The size of the ball seats incrementally increase from the toe to the heel. The smallest ball is dropped first to pass through all of the ball seats until it lands in the smallest ball seat at the toe and the bore is pressurized to shift the sleeve for opening ports therein. Stimulation, such as fracturing, is performed through the open ports. After the first stage has been stimulated, the next incrementally larger ball is dropped to land in the next uphole ball seat to shift the next sleeve valve for stimulating the next stage.
Such operations can be performed in open hole completions, where annular packers are positioned between stages to isolate the annular space between the completion string and the wellbore. Operations can also be performed in cemented completions where cement is used to fill the annular space for isolating between the stages.
To date, such systems have relied on the balls, engaged in the respective seats, to isolate the bore of the completion string below the stage being stimulated, preventing fluids from being directed and lost to the open ports therebelow. However, should the pressure upstream of the ball be sufficiently high, the pressure differential developed across the ball has been known to cause the ball to be extruded through the ball seat or the ball seat may fail, resulting in a loss of stimulation fluid to the open ports therebelow and the inability to effectively stimulate that stage. In this case, the operator can accept the failure of the ball/ball seat and move to the next stage, accept the failure and continue the stimulation in hopes some of the stimulation fluid enters the intended stage or drop another ball of the same size to try to shift the sleeve and stimulate the intended stage. In each case, time, complexity and costs increase. Efforts to prevent extrusion, such as increasing the size of each ball relative to the size of the respective seat or to decrease the size of the seat, has limited the incremental increases in ball size and hence, the number of stages that can be stimulated in a single operation. Further, if lower pressures are used to keep the pressure differential in a range to avoid extruding the balls, there may be insufficient pressure to perform the stimulation.
There is interest in the industry to be able to not only open sleeves but also to close sleeves. However in most prior art ball drop systems, the actuation is limited to a downhole action and therefore, it is not possible or practical to close the sleeve. An ability to close the sleeve permits much greater control over fluid delivery to and from the wellbore. It may be desirable to close the sleeve to allow the fractures to heal following treatment, to prevent sand, water and/or gas from entering the wellbore or to close off lower stages to prevent high differential pressures across the ball to minimize ball failure.
Accordingly, in the industry, conveyed shifting tools are known for opening and closing sleeve valves. Generally a shifting tool, having a profile formed thereon, is deployed into the completion string for engaging in a corresponding profile in the sleeve. Thereafter, the shifting tool is manipulated to push or pull the sleeve for opening and/or closing of the sleeve valve. Wellbore access for use of shifting tools in ball drop systems requires the stimulation operation to be stopped and the tool run in to the completion string to shift one or more sleeves and then tripped out of the wellbore. Such operations add to the cost and complexity of performing the stimulation operation.
One additional problem that is encountered in production after stimulation operations, particularly fracturing, is the large amount of sand or other particulates, including formation fines, produced with the hydrocarbon. Generally, surface equipment is used to separate sand from the produced fluid which adds to the overall cost of production. Downhole screens are known for use in operations such as Steam Assisted gravity Drainage (SAGD) and are generally installed on the outside of the horizontal sections of the production wellbore for production of fluids therealong. Further, screens are installed at the bottom of productions strings in wellbores known to produce large amounts of sand or in inflow control devices (ICD), which address non-uniform production profiles using a series of restrictions or nozzles therealong to maintain a more equal pressure drop from the formation to the wellbore for optimizing production therealong.
In fracturing operations, the presence of a screen extending over ports intended for delivering fracturing fluid including proppant therein, would render the ports inoperative. Production of sand-laden fluids, such as following a fracturing operation, would likely result in sanding off of the screen, particularly when a single screen is used at the end of the production string. Further still, nozzles in an ICD are unsuitable for delivery of fracturing fluids as the proppant would damage the restrictions as a result of erosion. Furthermore, as all ICD's remain open, it would not be possible to direct treatment fluid to one particular device at a time.
There is interest in the industry for systems and methods which allow ports to be closed following stimulating each stage without adversely affecting the efficiency of the stimulation operation. Further, there is interest in efficient and cost effective means for controlling sand production during production and more particularly following stimulation operations.